It is possible to form a structure having a fine structure on a substrate formed of silicon or the like, by using a fine processing technology which is used in a process of forming a semiconductor integrated circuit, and the technology is expected to be developed in future. Such a structure is referred to as MEMS (Micro Electro Mechanical System(s)). Various sensors and actuators have been proposed as the MEMS until now.
Patent Literature 1 discloses a pressure sensor having a cantilever. The cantilever is a bending member having a fixed end and a free end, and is also referred to as a cantilever beam. In the pressure sensor, an air chamber is provided in a lower side of the cantilever, and an upper side of the cantilever is the outside (atmosphere). The cantilever is manufactured so as to exert a piezoresistive effect. A gap (clearance) is formed around the cantilever, and the air chamber is connected to the outside through the gap. Specifically, the air can flow between the air chamber and the outside through the gap. When a pressure difference appears between the upper side and the lower side of the cantilever, the cantilever is deformed, and the deformation is detected as a change of a piezoresistance value. The pressure difference is solved by a movement of the air through the gap, and finally a pressure balance state appears. This structure disclosed in Patent Literature 1 can obtain sensitivity higher than a diaphragm type sensor.
In FIG. 15 in Patent Literature 2, a biosensor having a cantilever is disclosed. An air chamber is provided in a lower side of the cantilever, and a micro flow channel which accommodates a liquid therein is formed in an upper side of the cantilever. A slit which is clearance is formed around the cantilever. An interface between the liquid and the gas is formed in the inside of the slit. Specifically, a surface tension of the liquid, and/or the like prevent the liquid from entering the gas chamber. When a specific substance existing in the micro flow channel becomes attached to the surface of the cantilever, a resonance frequency of the cantilever changes. The change of the resonance frequency is measured with a laser Doppler meter. Incidentally, in the structure disclosed in FIG. 1 in Patent Literature 2, there exists an open space (air layer) in the lower side of the cantilever.